Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

160
FXUS63 KLOT 020535
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1235 AM CDT Sat May 2 2026

.KEY MESSAGES...

- Widespread frost development is expected tonight into
  Saturday morning across portions of northern IL and northwest
  IN.

- There is a low (~15-20%) chance for showers and thunderstorms Sunday
  followed by a better (~30-40%) chance for thunderstorms on
  Monday.

- Outside of a brief warmup early next week, near to below
  normal temperatures are favored through next week with
  occasional chances for rain showers.

&&

.UPDATE...
Issued at 916 PM CDT Fri May 1 2026

Have expanded frost advisory slightly into La Salle and Grundy
counties for tonight, and lowered temps slightly into these
areas with clear/partly cloudy skies and weak surface ridge axis
resulting in light/calm winds.

Broad upper level trough remains in place across the Great
lakes and upper Mississippi Valley region this evening, though
the main trough axis will shift southeast of the area into early
Saturday morning. Mid-level height rises already noted in the
wake of a couple of embedded short waves which are moving east
of the area this evening, with the associated subsidence and
loss of low-level instability with sunset helping to scatter out
the extensive stratocu deck from this afternoon. Weak surface
high pressure ridge is expected to develop into the forecast
area overnight in response, and the combination of mostly clear
to partly cloudy skies, light winds and a cool air mass setting
up conditions for widespread frost to develop by morning across
much of the forecast area. Given current trends, have lowered
temps a bit farther south into the I-80 corridor west of Chicago
overnight, and have expanded the frost advisory slightly to
include La Salle and Grundy counties.

Otherwise, quiet weather conditions are expected into Saturday,
with no other significant changes made to the forecast at this
time.

Ratzer

&&

.DISCUSSION...
Issued at 205 PM CDT Fri May 1 2026

The broad upper low continues its vacation over the Great Lakes
with a shortwave disturbance pivoting along the low`s western
periphery in IA, WI, and southern MN. This shortwave has lead to
the development of partly to mostly cloudy skies across
northern IL and northwest IN this afternoon and may even give
way to a few isolated showers as well. While recent radar trends
do show some light echoes developing in eastern IA, northwest
IL, and southern WI; none of them are reaching the ground at
this time. However, with dew points across the area mixing down
into the upper 20s and lower 30s confidence on showers actually
being able to reach the ground has diminished. Nevertheless,
have opted to maintain the slight (15-20%) POPs in the forecast
for now. Otherwise, expect temperatures to remain in the lower
50s for most with mid to upper 40s near the lake.

Any showers that develop this afternoon will taper shortly
after sunset as the shortwave pivots east. Skies behind the wave
should quickly clear as modest height rises and a weak surface
high moves overhead. The combination of clearing skies, light
winds, and cooling temperatures into the low to mid-30s will
result in widespread frost development across much of the area
tonight. Therefore, a Frost Advisory remains in effect for late
tonight into Saturday morning for most of northern IL and
northwest IN. The exception however is for Central Cook County
(downtown Chicago) and our southwest CWA where milder
temperatures and lingering cloud cover may limit frost coverage.

The modest ridging will persist through Saturday night which
will keep dry conditions in play to start the weekend. However,
the continued northwest winds will keep highs only in the mid to
upper 50s inland and in the upper 40s to lower 50s near the
lake. With the ridging overhead it seems skies should favor a
mostly to partly sunny conditions which may once again lead to
some patchy frost development Saturday night into Sunday
especially in northwest IN.

The forecast for the Sunday through Tuesday timeframe remains
generally unchanged but there is a lot of uncertainty in the
exact timing of the key features. The upper low and associated
troughing over the Great Lakes is forecast to shift east on
Sunday which will allow a couple of shortwave troughs to dig out
of Canada and into the region. At the same time, another
trough/upper low is forecast to develop off the southern CA
coast and should begin to move inland Monday into Tuesday. These
features will help to generate stout southwesterly flow across
northern IL and northwest IN on Sunday which will lead to a
slight warming trend with highs in the mid to upper 60s forecast
areawide Sunday afternoon. This warm advection in addition to
the forcing from the leading shortwave looks to be sufficient to
generate at least some isolated to widely scattered showers and
perhaps a few thunderstorms on Sunday. While most guidance
continues to favor a later afternoon and evening timeframe for
the higher rain chances Sunday, recent guidance trends have
started to hint at a faster shortwave arrival which could lead
to some showers developing Sunday morning. Given the
inconsistencies run to run in guidance have opted to just
maintain the low chance (~20%) POPs for the entire day on Sunday
for now but suspect some dry hours are possible. Outside of the
rain, winds on Sunday will be breezy with gusts likely around
30-35 mph especially during the afternoon.

The better chances for rain are still expected to occur with
the passing of the more amplified secondary shortwave and its
associated cold front late Monday into Tuesday. With guidance
trending later with the frontal passage, it appears likely that
highs on Monday will top out in the 70s areawide courtesy of the
continued breezy southwest winds. Despite there being a
stronger signal for a later frontal arrival, there continues to
be uncertainty as to the degree of moisture return ahead of the
front which will dictate the coverage and intensity of
thunderstorms. Regardless, a fair coverage of showers and
thunderstorms is expected for Monday especially during the
afternoon and evening hours. Given that moisture still looks to
be a limiting factor the threat for any severe weather continues
to look low, but if more moisture is able to advect in then
that may change considering that 35-40 kts of deep shear are
forecast to be present.

The cold front is progged to shift south of the area late
Tuesday which is expected to return cooler temperatures to the
region as broad troughing redevelops over the Great Lakes. Thus,
highs in the 50s (locally cooler near Lake Michigan) can be
expected for the middle and later half of next week.
Additionally, periodic shortwave disturbances will continue to
dive through the broader trough and result in occasional chances
for showers especially towards the later half of next week.

Yack

&&

.AVIATION /06Z TAFS THROUGH 12Z SUNDAY/...
Issued at 1235 AM CDT Sat May 2 2026

No significant weather concerns for aviation through this
evening. While there could be some patchy shallow light ground
fog at DPA and RFD early Saturday morning, the current most
likely worst case scenario is that VSBY could briefly get to
MVFR around and just past sunrise.

Light winds will become northwest after sunrise. Guidance has
been trending slightly strong with the westerly wind component
this afternoon, which suggests the lake breeze may remain east
of ORD/MDW/DPA.

- Izzi

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Frost Advisory until 8 AM CDT this morning for ILZ003-ILZ004-
     ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-
     ILZ020-ILZ021-ILZ023-ILZ033-ILZ103-ILZ105-ILZ106-ILZ107-
     ILZ108.

IN...Frost Advisory until 8 AM CDT /9 AM EDT/ this morning for
     INZ001-INZ002-INZ010-INZ011-INZ019.

LM...None.

&&

$$

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